Abstract100 genotypes of
Triticum aestivum L. were screened in a plastic tunnel for heat
tolerance by providing them heat stress at the time of anthesis.
Selection of the genotypes was based on grain weight, number of
grains per spike and grain yield per 25 spikes after computation of
their relative ratios. The selected genotypes were also tested by
measuring their electrolyte leakage to confirm the tolerance and
susceptibility by calculating relative injuries. Seven genotypes
including 3 heat tolerant, 1 moderately tolerant and 3 susceptible
were crossed in a 7 × 7 diallel fashion including direct and
reciprocal crosses in a randomized complete block design with three
replications in two sowing dates. One set of these genotypes was
sown under normal environmental conditions and other set was sown
under heat stress conditions to provide temperature stress to these
genotypes atthe time of anthesis. Data of various morphological
characters was taken at different stages of the growth period of the
crop and then subjected to statistical analysis. Significant
variation was found among parents and their offspring. Gene action
and the percent increase or decrease of F1 hybrids over mid parent
as well as better parent value was calculated to estimate possible
heterotic effects for yield and its components. Scaling tests were
used to test the adequacy of the data for analyzing the
additive-dominance model which showed that the additive-dominance
model was fully adequate for plant traits like flag leaf area, RCI
%, spike weight, spikelets per spike, number of grains per
spike, biomass per plant and grain yield under normal conditions and
for characters like
plant height, flag leaf area, relative cell injury (%), days to
maturity, number of grains per
spike, 100-grain weight and harvest index under heat stress
indicated that dominance was
present and epistasis was absent. All the remaining traits exhibited
partial adequacy under
both the conditions. The results of the genetic studies showed that
almost all the traits
show additive genetic effects with partial dominance and with
moderate to high
heritability. Relative cell injury (%) calculations revealed that
this is an efficient tool for
screening against heat.Some of the hybrids like Maya/Pavon ×
Punjab-85, Maya/Pavon ×
Chenab-2000 and Shalimar-88 × Weebli-1 showed very useful results
with relative
injuries even less than their parents. The results of heterosis
suggest that hybrid vigour is
available for the commercial production of wheat and selection of
desirable hybrids
among the crosses having heterotic and heterobeltiotic effects in
other characters is the
best way to improve the grain yield of bread wheat. The cross
combinations like Inqilab-
91 × Shalimar-88, Shalimar-88 ×Maya/Pavon, Chenab-2000 × Punjab-85,
Maya/Pavon ×
Chenab-2000, Shalimar-88 × Uqab-2000 and Uqab-2000 × Maya/Pavon are
the best
hybrids which can be further exploited because of their ability to
perform well under
normal and even diverse environments. Maximum heterosis (24.24%) and
heterobeltiosis
(19.95%) for number of grains per spikes was shown by the cross
combination, Inqilab-
91 × Maya/Pavon under normal conditions and under heat stress
maximum heterosis
(36.13%) and heterobeltiosis (13.66%) was shown by the cross
combinations Punjab-85 ×
Chenab-2000 and Weebli-1 × Uqab-2000 respectively. For 100-grain
weight maximum
heterosis (28.22%) and heterobeltiosis (27.87%) was recorded for
cross combination
Chenab-2000 × Inqilab-91. However, under stress Inqilab-91 ×
Weebli-1 (23.35%)
followed by Maya/Pavon × Uqab-2000 (13.28%). Maximum heterosis
(28.70%) and
heterobeltiosis (15.58%) for grain yield per plant was shown by the
cross Uqab-2000 ×
Punjab-85 under normal conditions but under stress Uqab-2000 ×
Chenab-2000 produced
maximum heterosis (27.02%) and maximum heterobeltiosis (13.62%) was
shown by the
cross Shalimar-88 × Uqab-2000. The information obtained from these
results during the
current studies may be used to evolve high yielding varieties which
can produce
economic yield and help maintain yield sustainability in those areas
where terminal heat
stress is a major threat.